use seperate config for amavis-dkim-config even is the systems uses a monolith config to prevent overwriting the key-config during updates

Fixed #4667 Websites UI / Let's Encrypt :: add Option to allow switching to fullchain.pem in favor of chain.pem

- typo

Improved the code that generates the ssh keys for clients and shell users and reorganized it into a central function.

- fixed some smaller things in plugins for apache and nginx

Implemented #4271 Creating vHost Website Alias copies default index.html thus breaking the original site if it's based on index.php (or something not index.html)

- Added missing shell escaping